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Supernovae May Explain Mass Extinctions of Marine Animals During Pliocene Era (theregister.co.uk)
"The Register has an article on the possibility that a supernova or a series of them could explain a mass die-off of marine animals around 2.6 million years ago," writes Slashdot reader KindMind. From the report: A gigantic supernova explosion may have triggered mass extinctions for creatures living in Earth's prehistoric oceans some 2.6 million years ago, according to new research published in Astrobiology. Marine animals like the megalodon [...] suddenly disappeared during the late Pliocene. Around the same time, scientists [...] noticed a peak in the iron-60 isotope in ancient seabeds. "As far back as the mid-1990s, people said, "Hey, look for iron-60. It's a telltale because there's no other way for it to get to Earth but from a supernova.' Because iron-60 is radioactive, if it was formed with the Earth it would be long gone by now. So, it had to have been rained down on us" explained Adrian Melott, lead author of the paper and a physics and astronomy professor at the University of Kansas.
The team believes that a supernova located 150 light years away set of a chain of supernovae bursts and covered the Earth in a shroud of deadly cosmic ray radiation. This was amplified, Melott said, because the Solar System is right on the edge of an area of the interstellar medium called the Local Bubble. The Local Bubble extends about 300 light years across and contains the two main clouds of dust and gas: Local Interstellar Cloud and the G-Cloud. As the supernovae ejected cosmic rays, these beams of energetic particles would have repeatedly bounced off the clouds to create a "cosmic-ray bath" that could have lasted 10,000 to 100,000 years. Some of that radiation such as cosmic ray muons would have leaked onto Earth, and over time it could have led to genetic mutations and cancers [that would have caused animals like the megalodon to die off prematurely].
The team believes that a supernova located 150 light years away set of a chain of supernovae bursts and covered the Earth in a shroud of deadly cosmic ray radiation. This was amplified, Melott said, because the Solar System is right on the edge of an area of the interstellar medium called the Local Bubble. The Local Bubble extends about 300 light years across and contains the two main clouds of dust and gas: Local Interstellar Cloud and the G-Cloud. As the supernovae ejected cosmic rays, these beams of energetic particles would have repeatedly bounced off the clouds to create a "cosmic-ray bath" that could have lasted 10,000 to 100,000 years. Some of that radiation such as cosmic ray muons would have leaked onto Earth, and over time it could have led to genetic mutations and cancers [that would have caused animals like the megalodon to die off prematurely].
So any evidence of dinosaur cancers, or are we just making shit up now because maybe?
There were no dinosaurs in the Pliocene (5.3 to 2.6 mya). The dinosaurs died out roughly 70 million years ago (except for birds).
The supernova hypothesis is not just conjecture. The Scorpius Centaurus star cluster passed close (150 ly) to earth during the Pliocene, and there are remnants of supernovae from about that timeframe. The iron isotopes are more evidence.
There are other explanations for the extinctions. The Isthmus of Panama formed about that time, which changed ocean currents and may have disrupted migration paths. The climate was cooling and the ice caps formed. As the ice caps freeze and thaw they change salinity (creating cold saline water that sinks to the depths with they freeze, and brackish surface water when they thaw), and more extreme thermal gradients, as cold and saline polar "bottom water" settles into the ocean depths. This changes currents and reduces upwelling.
It could have been any of these factors, or some combination of all of them. The Pliocene extinctions were not sudden like the Permian and Cretaceous-Tertiary extinctions.
I am curious as to why this would have driven marine animals to extinction without having a similar effect on terrestrial animals. I would want this explained before giving this theory any credence.